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[NaryReassociate] Run EarlyCSE after NaryReassociate

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Summary:
This patch made two improvements to NaryReassociate and the NVPTX pipeline

1. Run EarlyCSE/GVN after NaryReassociate to get rid of redundant common
expressions.

2. When adding an instruction to SeenExprs, maps both the SCEV before and after
reassociation to that instruction.

Test Plan: updated @reassociate_gep_nsw in nary-gep.ll

Reviewers: meheff, broune

Reviewed By: broune

Subscribers: dberlin, jholewinski, llvm-commits

Differential Revision: http://reviews.llvm.org/D9947

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238396 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Jingyue Wu
2015-05-28 04:56:52 +00:00
parent 9dacaea1a1
commit 4977e92629
3 changed files with 48 additions and 10 deletions
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lib/Transforms/Scalar/NaryReassociate.cpp
+23 -1
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@@ -234,6 +234,7 @@ bool NaryReassociate::doOneIteration(Function &F) {
BasicBlock *BB = Node->getBlock();
for (auto I = BB->begin(); I != BB->end(); ++I) {
if (SE->isSCEVable(I->getType()) && isPotentiallyNaryReassociable(I)) {
const SCEV *OldSCEV = SE->getSCEV(I);
if (Instruction *NewI = tryReassociate(I)) {
Changed = true;
SE->forgetValue(I);
@@ -243,7 +244,28 @@ bool NaryReassociate::doOneIteration(Function &F) {
}
// Add the rewritten instruction to SeenExprs; the original instruction
// is deleted.
SeenExprs[SE->getSCEV(I)].push_back(I);
const SCEV *NewSCEV = SE->getSCEV(I);
SeenExprs[NewSCEV].push_back(I);
// Ideally, NewSCEV should equal OldSCEV because tryReassociate(I)
// is equivalent to I. However, ScalarEvolution::getSCEV may
// weaken nsw causing NewSCEV not to equal OldSCEV. For example, suppose
// we reassociate
// I = &a[sext(i +nsw j)] // assuming sizeof(a[0]) = 4
// to
// NewI = &a[sext(i)] + sext(j).
//
// ScalarEvolution computes
// getSCEV(I) = a + 4 * sext(i + j)
// getSCEV(newI) = a + 4 * sext(i) + 4 * sext(j)
// which are different SCEVs.
//
// To alleviate this issue of ScalarEvolution not always capturing
// equivalence, we add I to SeenExprs[OldSCEV] as well so that we can
// map both SCEV before and after tryReassociate(I) to I.
//
// This improvement is exercised in @reassociate_gep_nsw in nary-gep.ll.
if (NewSCEV != OldSCEV)
SeenExprs[OldSCEV].push_back(I);
}
}
}